A computer typically relies on several steps to boot. Those skilled in the art are familiar with the typical boot process for a computer such as a personal computer. The basic input output system (BIOS) or other firmware boot code initializes the system which then initializes any devices (e.g., network, hard disk, or compact disc) from which to boot. At this point, the system initializes local boot code and launches a boot environment. The boot environment provides operating systems services or other resources to applications. The boot environment enables additional operations to be performed such as installing a software image of an application program (e.g., a word processing application program or a spreadsheet application program). However, the boot environment is often too large to be stored along with the software image on most computer-readable media. For example, with a software image size of 600 megabytes (MB) and a boot environment size of 150 MB, the 750 MB total exceeds the 680 MB maximum for optical media per ISO 9660.
Some existing systems provide a layered file system in which one layer compresses all data before writing it out to a medium and uncompresses all data read from the medium to save space on the medium. Such a file system may be implemented as a layer on top of a base file system existing on the medium. For example, such a system may mount a compressed tape archive (e.g., tar) file. However, such a system fails to provide a compressed, bootable software image.
Further, some existing systems allow a computer to boot from a compressed kernel. However, the kernel does not provide a rich boot environment such as provided by a minimal operating system. Other systems save a compressed image of an operating system in an extended memory area of a computer's physical memory and then boot (e.g., “soft boot”) the computer from that static image. Still other systems compress portions of an operating system in a read-only memory image and execute the system from the compressed image. Yet other systems boot a system by first executing uncompressed BIOS code to enable memory and then uncompressing BIOS code as needed to complete the boot. However, these systems lack the ability for a computer to be able to boot from an image of a boot volume that is compressed, to reduce random access memory overhead on the computer, and to boot on any standard personal computer using standard boot firmware. Further, the existing systems lack the flexibility of having the compressed image exist as a file.